digitalocean-import: Fix panic when 'image_regions' not set (Fixes: #7843).

post-processor/digitalocean-import/post-processor.go

@@ -119,7 +119,6 @@ func (p *PostProcessor) Configure(raws ...interface{}) error {
 		"spaces_region": &p.config.SpacesRegion,
 		"space_name":    &p.config.SpaceName,
 		"image_name":    &p.config.Name,
-		"image_regions": &p.config.ImageRegions[0],
 	}
 	for key, ptr := range requiredArgs {
 		if *ptr == "" {
@@ -128,6 +127,11 @@ func (p *PostProcessor) Configure(raws ...interface{}) error {
 		}
 	}
 
+	if len(p.config.ImageRegions) == 0 {
+		errs = packer.MultiErrorAppend(
+			errs, fmt.Errorf("image_regions must be set"))
+	}
+
 	if len(errs.Errors) > 0 {
 		return errs
 	}